Substrate bias circuit

Claim 1

A substrate bias circuit comprising: an oscillation circuit oscillating at a predetermined frequency; a control signal generation circuit operative to generate a control signal for changing, on the basis of an output from said oscillation circuit, a substrate potential in a direction to ensure a threshold level of a transistor so that it becomes greater; and a charge pump circuit including a capacitor and operative in response to said control signal to control the charge and discharge of said capacitor by to thereby change said substrate potential at two stages; wherein said charge pump circuit comprises: a capacitor series circuit comprised of said first mentioned capacitor and second capacitor connected in series through a first transistor, a second transistor for which conduction is controlled by a potential at the junction of said first transistor and said second capacitor, and operative to introduce a potential on the output terminal of said charge pump circuit to the junction of said first transistor and said first capacitor; a third transistor for introducing a potential at the junction of said first transistor and said first capacitor; a third transistor for introducing a potential at the junction of said first transistor and said first capacitor to a reference potential terminal; a first gate control circuit operative to control a gate voltage of said third transistor to allow said second and third transistors to be interchangeably conductive; and a second gate control circuit operative to allow said first transistor to be conductive within a time period during which said second transistor is non-conductive, to cause a change of the substrate potential of said second stage.